They're not. These are maps of the wifi and ISP connections each UUID connects via, not individual location. The generalized location can be inferred but no specific individual device is tracked.
This tracks world wide. . . and Android tablets are not seen in the wild as much. I saw some toy tablets offered the other day with Android: 5" screens and Froyo OS . . . $19.95. No WIFI, BLUETOOTH , or any connectivity at all. Ran on two AA Batteries. It STILL counts as competition for the iPad even though these are not targeting the same customer demographics. Absurd conclusion.
I disagree, in the courts android tablets are now more common than ipads due to cost.